As a solder alloy, an Sn—Pb-based alloy has been generally used. The Sn—Pb-based alloy has the eutectic point of 183° C. at a composition of Sn-37Pb (37% by weight of Pb and the balance of Sn), and the melting temperature thereof can relatively significantly be varied by adjusting the composition of Sn—Pb. The solder materials used to, for example, connect an electronic component(s) to a substrate are roughly classified based on the temperature at which the solder alloy in the solder material can be melted (the solder connecting temperature) into solder materials directed to use at a middle to low temperature (up to 250° C.) and solder materials directed to use at a high temperature (about 250 to 350° C.), and can each properly be selected according to an application of products that are finally obtained.
It is however socially required to substitute lead-containing solder alloys with lead-free solder alloys (so-called “elimination of lead”) taking into consideration that lead included in Sn—Pb-based alloys may cause environmental pollution due to improper waste treatment.
As the lead-free solder alloys, Sn-based solder alloys such as, for example, an Sn—Ag-based, an Sn—Cu-based, and an Sn—Ag—Cu-based solder alloys are currently developed. These solder alloys have a relatively low melting point (up to 230° C.) and are therefore practically used in solder materials directed to use at a middle to low temperature.
As one of other lead-free solder alloys, there is known to be a Bi-based lead-free solder alloy, and this solder alloy has a relatively high melting point (see Patent Literatures 1 to 3).